Considerable difficulty has been encountered in wellhead shearing devices on wells containing sour gas such as hydrogen sulfide because, while the cutting edges for adequate shearing should have a hardness greater than 24 to 26 Rockwell C, alloy steel of such high hardness is embrittled by exposure to hydrogen sulfide when under stress. This is commonly referred to as sulfide stress cracking.
U.S. Pat. No. 4,081,027 proposes to solve this problem by having the structural components with a maximum hardness of 22 Rockwell C and hard facing the cutting edges. The structure shown in FIG. 5 of this patent has been tested with only minimal success.
In other fields, it is well known to insert hard metal into the tip of tools to provide a wear resistant and hard metal cutting surface as shown in U.S. Pat. Nos. 3,888,027 and 3,834,764.
However, even with the knowledge of such prior art, difficulties continue to be encountered in wellhead shearing devices which are exposed to sour gas.